Fix build issues on Codespaces.

Author: ZCG-coder

CMakeLists.txt

@@ -59,18 +59,18 @@ IF(${OPERATING_SYSTEM} MATCHES "Android")
     SET(LINUX CACHE INTERNAL "Is Linux or Android" 1)
 ENDIF()
 
-IF(WIN32)
+IF(CMAKE_SYSTEM_NAME STREQUAL "Windows")
     ADD_COMPILE_DEFINITIONS(WINDOWS NOMINMAX) # Do not add min() and max() macros.
     IF(MSVC) # MSVC Has no UTF-8 support by default
         ADD_COMPILE_OPTIONS(/utf-8)
     ENDIF()
     SET(WINDOWS TRUE)
-ELSEIF(APPLE)
+ELSEIF(CMAKE_SYSTEM_NAME STREQUAL "Darwin")
     ADD_COMPILE_DEFINITIONS(MACOSX)
-ELSEIF(LINUX)
+ELSEIF(CMAKE_SYSTEM_NAME STREQUAL "Linux")
     ADD_COMPILE_DEFINITIONS(LINUX)
 ELSE()
-    MESSAGE(ERROR "Platform not defined")
+    MESSAGE(WARNING "Platform not defined")
 ENDIF()
 
 IF(CMAKE_BUILD_TYPE STREQUAL "Debug")